The deficit of the isometric tetanic tension redeveloped after a release of frog muscle at a constant velocity.

Abstract

Frog sartorius muscles tetanized isometrically were released at a constant velocity from lengths lL to ls (A/ = l L -ls; ls >/0). The tension P~s redeveloped after the release was lower than the isometric tension Ps at Is, and higher than the isometric tension PL at lL. The tension deficit D is defined as the difference Ps-P*. The timing of the release during the tetanus did not influence D. D/Po was proportional to Al/lo. The proportionality constant k was equal to 1.35 -+ 0.19 (n = 8) when the velocity of release was 2.5 mm/s. When the muscles were released the same Al, D was found to be an exponential decreasing function of the velocity. The tension deficit was also found in experiments performed in the region ls < lo. The proportionality constant k was smaller, but the influence of the velocity of the release on D was not modified. When the velocity of the release was changed during the release, D changed accordingly, showing that the effects of Al and V are multiplicative. These facts suggest a working hypothesis based on the concept that the actin filaments which enter the overlap region during a release are strained by the tetanic stress and therefore unable to make normal cross-bridges.

Variation in isometric force after active shortening and lengthening and their mechanisms: a review

“…amount of force obtained in isometric contraction of reference. These speculations are in agreement with the results obtained in some studies (2,6,7,19,32,43).…”

“…This would occur in sites located in two helices of the F-actin chain, which suffer an angular distortion that produce rotation as the muscle is shortened at low speed. Thus, the active site of actin binding is displaced from its original position, preventing the head coupling of heavy mero-myosin or MCP chain (6,7,33,43,44). The proponents of this hypothesis propose that an increase in the rate of cross-bridge uncoupling and an angular distortion, high enough to modify the organization, the structural arrangement and the ideal overlap between the actin-myosin quantity, alter the optimal sarcomere length.…”

“…Such a change would be sufficient to induce a deformation in the active sites of actin-myosin. These then would substantially reduce the number of available cross-bridges, as well as the tension generated by each cross bridge (6,7,32,33,34,43,45,46,47,48,49).…”

Contractile Performance of Striated Muscle

“…However, there has been a continuous search for alternative explanations and several imaginative mechanisms have been proposed (e.g. Maréchal & Plaghki, 1979;Sugi & Tsuchiya, 1988;Granzier & Pollack, 1989;Schachar et al, 2004). The phenomenon of force depression by loaded shortening was revisited by Edman, Caputo & Lou (1993) in frog single muscle fibres using a combination of supplementary techniques to elucidate the possible role of non-uniform sarcomere behaviour.…”

Parameter interdependence and success of skeletal muscle modelling

“…The fact that shortening has a decremental effect on muscle force during subsequent isometric contractions has been known for decades (Buchtal and Kaiser, 1951;Abbot and Aubert, 1952;Deleze, 1961;Bahler et al, 1968;Joyce and Rack, 1969;Marechal and Plaghki, 1979;van Ingen Schenau et al, 1988) but has found almost no application in muscle and movement modelling. This effect is present regardless of the nature of the shortening phase of the contraction (isokinetic or isotonic contraction).…”